Abstract Virtually complete charge transfer can be achieved with charge coupleddevices(CCDs)intheburiedchannelconfigurationbecausetheburiedchannelCCDintroduces no transfer noise. However, conventional charge detectors incorporatedinto CCDs have a comparably large noise, which consists of thermal noise and 1/fnoisefromMOS transistorin theoutputchargedetectors.
10Low-NoiseElectronicImagingwithDouble-GateFETs
Fig.10.5Potentialpro les
alongthedirection
perpendiculartodevice
surface223
thepotentialpro lesalongthedirectionperpendiculartothesurface.ThesolidlineandthedottedlinearethoseundertheFPPandundertheoutputgate(OG),respectively.Theabruptpotentialpro leunderthesensingchannelisessentialforthesignalchargeinthesensingchanneltomodulatethedetectiontransistorchannelconductanceeffectively.ThesourceanddrainregionsoftheP-channeldetectiontransistoraremadebyself-alignmentwiththeoutputgate(OG),resetgate(RS)andtheFPP.ThesourceisconnectedtotheP-channelloadtransistormadebyajunction-typeFETincorporatedintothesamechip.ThejunctionFETissuperiorforsuppressing1=fnoisecomparedtoaMOS-FET[4]
Acharge(electron)packettransferredintothesensingchannelthroughtheoutputgate(OG)isconvertedtoavoltagesignal,usingthe rststagesource-followerwhichconsistsofthedetectiontransistorandtheloadtransistor.Anoutputsignalisgeneratedusingthesecondstagesource-followerconstructedwithn-channelMOStransistors.Toremovethecharge(electron)packetfromthesensingchannelregionintoresetdrain(RD),apositivepulseisappliedtotheresetgate(RS).Thenthesensingchanneliscompletelydepletedinaso-called“transferoperation.”Thus,thedetectorhasnoresetnoise[5–7].
10.2.1.2DeviceSimulation
Atwo-dimensionaldevicesimulatorwasutilizedfordesigningthedetector.Inaconventionaldetector,aneffectivesensingcapacitanceisdeterminedapproximatelybythegateoxidecapacitanceofadetectiontransistor[2,3].Forhighsensitivity,lowsensingcapacitancehasbeenachievedbyemployinga1 mthickgateoxideforthedetectiontransistor.Figure10.6ashowsasimulatedpotentialpro leforelectronsinthedetectingsection.Apotentialpocketisobservedattheedgeoftheoutputgate(OG).Thepotentialpocketcausesnotonlycharge(electron)transferlossbutalsotransfernoise.Toeliminatethepocket,theFPPhasbeeninsertedunderthepotentialcontrolgate(G).Thepotentialpro leinthenewdetectorwiththeFPPisshowninFig.10.6b.Thepotentialpocketvanishes,whichenablesthenewstructuretoobtainreducedtransferlosssuf cientfortherealizationofalow-noisedetector.
